Blueprinting
your Kart Engine!
Blueprinting
your Kart Engine could be deemed to mean to bring the engine
to or close to the official specification as defined in the
rule book.
It is in fact the method of making the racing engine conform
to the original blueprints or plans which the engine is manufactured
from. No doubt you are wondering why the engine you just paid
a large sum of money for, is not already made according to
the official specifications.
TOLERANCES
The answer
to that is in the manufactures tolerances. A manufacturer
such as Yamaha, will manufacture the KT100 S according to
given tolerances, you know, plus or minus .05 etc., that sort
of thing. The engines could be manufactured to exact tolerances,
but then of course you would be paying a great deal more for
your engine, because in order to manufacture to such exact
tolerances, the manufacturer would need even more expensive
machines than he is using already and the quality checks would
be extremely numerous and exacting.
An engine made to exact tolerances would need to be made under
the same conditions that the space shuttle was made and you
have read or heard of the costs involved in that program.
The resultant price of an engine made in this manner could
well approach $10,000. Interested in buying one? Manufacturing
tolerances do vary from day to day. Of course we have all
heard about the engine which was unbelievably fast straight
out of the box and that can happen, if that particular engine
has all the tolerances extremely close, however, that situation
does not happen very often.
Now you
have some idea of why blueprinting is necessary, read on for
some details on how it is done.
SQUARING
OFF
Probably
the most important of all blueprinting operations is to ensure
everything is square, i.e. getting the top of the crankcase
parallel with the crank, ensuring that the main bearings are
in line, the bottom of the cylinder is at right angles to
the bore, the conrod is straight, the crankshaft is square,
the bottom of the crankcase is square, etc.,
The importance
of having everything straight and square cannot be overemphasized.
If any of the components are not square or straight then you
have extra friction which causes extra heat and in turn causes
a drop off in performance. If all the parts are straight and
square then friction is kept to a minimum and the result is
the engine will perform at it's peak with heat and wear being
minimised. The blueprinting of a karting engine can be likened
to a chain, you know the old saying, a chain is only as strong
as it's weakest link, one weak link and disaster.
The place
to start (after completely disassembling and cleaning the
engine) is the crankcase. To square the crankcase the engine
builder will set up the case halves with a hardened ground
bar. The distance from the top of the bar to the top of the
cases is measured with a depth micrometer. Any difference
in the depth from side to side, means that the top of the
crankcase is not parallel with the bar (as substitute for
the crankshaft) and therefore, metal will need to be taken
off the high points until the measurements from the bar to
the top of the crankcase are identical from side to side.
It is
essential that the top of the crankcase is parallel to the
crankshaft, and that the barrel is square with the crankshaft
to ensure that the piston will run true, thus reducing wear
and increasing performance, because of the resulting reduction
in friction. The measurements from front to back are not so
critical, because the piston is able to rock back and forth
in that plane.
Various
methods are used by the various engine builders for taking
the metal off the various components. Some use a surface grinder,
others a milling machine, while still others use a lathe.
There is no one correct method, but the method is only effective
if it is carried out by a competent machinist. These operations
are performed to extremely close tolerances and only a competent
machinist can perform such work.
CRANKCASE
After
the top of the crankcase is trued, the crankcase is turned
over and the bottom is trued up to ensure that the engine
will sit squarely on the engine mount. An engine which is
not sitting squarely on the engine mount could cause problems
with chains, and sprockets, not to mention stress on the crankshaft
and the friction caused because of the incorrect mounting
of the engine, will undoubtedly cause a drop off in performance.
Now that
the crankcase is square top and bottom, the alignment of the
main bearings is checked by the use of a bar being slid through
both bearings together. Any stiffness here means the bearings
could be out of alignment and the engine builder will machine
the bearing housing to ease any binding, just as he will measure
the diameter and shape of the bearing housing. Any tightness
here could cause main bearing failure and believe it, the
failure can be rather dramatic. This machining of the bearing
housing is again very critical and should only be carried
out by a competent machinist.
If your
kart engine builder doesn't have the precision machines and
tools, as well as a competent machinist to carry out the necessary
work, look elsewhere. There are plenty who have.
Blue
printing is the most important job you do to your
racing kart engine, if it is not done correctly
then your engine will never perform to its peak capacity,
hence everything else you do with your kart could well turn
out to be a waste of money because your engine will let you
down in the final analysis.
